Protector for electric circuits



May 23, 1939. H. TA BussMANN A 2,159,423

PROTECTOR FOR ELECTRIC CIRCUITS Filed OCL. 5, 1936 2 Sheets-Sheet l t/////////`)//,/////////////////////////f/,//////////////A W3? gl t INVEN TOR. /sN/w 7.' ussMn/v/v ATTORNEY May 23, 1939 H. T. BUSSMANNPROTECTOR FOR ELECTRIC CIRCUITS Filed 0G13. 5, 1936 2 Sheets-Sheet 2INVENTOR. HENRY 7." ,B1/ss MAN/v BY K W ZM A TTORNE Y.

Patented May 23, 1939 UNITED STATES PATENT OFFICE 32 Claims.

My invention relates to electrical protective devices adapted to beincluded in an electric circuit and to blow and interrupt the circuitwhen the current therein exceeds a certain value for a certain length oftime.

An object of my invention is to provide such a device having longblowing times at overloads which could be maintained for relatively longperiods of time without resulting in injury to the circuit wiring or toany energy translating device forming apart of the circuit. 'Anotherobject of my invention is to provide such a device having the abovecharacteristics, but also capable of blowing almost instantaneously onsuch higher overloads as short circuits.

Another object of my invention is to provide` lsuch a device capable ofbeing enclosed in a fuse casing of standard size for its rating and,when so enclosed, of meeting the short circuit operating requirements asset forth in the Underwriters Laboratories Standard for Enclosed Fuses.

A still further object of my invention is to provide such a protectivedevice in a design equally vapplicable to high and to small currentratings.

To these and-other ends my invention consists in the novel features andcombinations of parts to be hereinafter described and claimed.

In the drawings,

Figure 1 is a view in longitudinal section through a cartridge type ofprotector embodying my invention,

Fig. 2 is an enlarged fragmentary view, in perspective, of a part of thestructure embodying my invention,

Fig. 3 is a view in longitudinal section of a modified form of d eviceembodying my invention,

Fig. 4 is a top plan view of a fuse strip such as may be used in thedevice shown in Fig. 3,

Fig. 5 is a view in longitudinal section through another form ofprotector embodying my invention,

Fig. 6 is a top plan view thereof with the window and closure memberremoved,

IFig. '1 is a longitudinal sectional View through another form ofprotector embodying my invention, and

Fig. 8 is a longitudinal sectional view through a still furthermodification of protector embodying my invention.

Referring to Fig. 1 of thef drawings, I have there illustrated acartridge type protector 2l comprising a casing 23 ofelectric-insulating material and of the usual cartridge fuse formhavng'ferrule terminals 25 and 21 thereon at the respective ends. Theseconducting ferrules may be secured by having the inner ends thereofcrimped or rolled inwardly as indicated at 29 or in any other suitablemanner.

'Ihe ferrule 21 has rigidly secured to the inside thereof a relativelyheavy metallic heat-conducting and heat-storing member 33 in order thatit may store a relatively large amount of heat or. may conduct heat awayfrom other parts of the `protector operatively associated therewith andto be hereinafter described in detail. The inner end of member 33 may beprovided with a slot 35 for a purpose to be hereinafter described.

A fuse link 31 has one end 39 thereof held in electrical engagement withthe member 33 and in Figs. 1 and 2 I have shown this electricalengagement as being maintained by a relatively small mass of heatsoftenable material such as low melting point solder 4l. I have shownthe fuse link 31 as being made of a single strip, extending over andbeyond the slot 35 and held in electrical engagement with the member 33adjacent to the inner end of the slot. The outermost end portion 39 ofthe fuse link may be bent slightly angularly relatively to the rest ofthe link in order to provide an anchorage for one end of a biasing oropening means 43 in the shape of a helical spring, the other end ofwhich is anchored to a small portion 45 of a disc 41 which may be madeof electric-insulating material, and is held at the end of therelatively massive member 33 by an offset portion I5 on the link .31.The fuse link extends through a suitable opening in the disc l1. I donot desire, however, to be -restricted to the particular details of theinner end portion of the relatively massive member 33 and the anchoringof one end ofthe biasing means 43, but have illustrated these only toshow one form of such devices which I may utilize.

The disc I1 divides the interior of the cartridge 'casing 23 into twoparts,- one part, a chamber 5l, being usually smaller than the otherpart on the other side of the disc and containing the heavy member 33,an end portion of the link 31, the small mass of heat softenablematerial Il and the spring means 43. The other part of the interior ofthe casing contains the major portion of the fuse link 31 and moreparticularly that part thereof which is adapted to fuse at apredetermined temperature when subjected to heavy overloads, includingshort circuits.

Ihat end of the heavy member 33 engaging the contact terminal 21 isattached thereto by soldering, riveting or by any other method whichwill maintain them in good electric and heat conducting relation witheach other. The other end of the fuse link is secured to the contactterminal 25 in any manner which will maintain them in electricalconnection under all operating conditions of the protector.

Referring now to Fig. 3 of the drawings, I have there illustrated acartridge type protector 53 including a cartridge casing 55 havingferrules 51 thereon at the respective ends and being provided with knifeblade terminals 59 and 6|, respectively. A fuse strip 63, which has afusing portion B5 therein at substantially the middle of its length, hasone end secured in electrical engagement with the inner end of knifeblade 5.9 as by a mass 61 of ordinary solder or it may be riveted orotherwise permanently secured thereto. The other end of the fuse link 63has y a short longitudinal slot therein .to provide two hard solder,riveting or any other suitable manner.

The end portion 1| may be suitably arranged to permit of securingthereto one end of an operating means 11, here shown as a helicalspring, the other end of which is secured to a disc 19, which is at theinner end of the contact terminal 6| and divides the casing 55 into twochambers. One of these chambers contains the inner end of contactterminal 59, the major portion of the link including the fusing portion65 and an arc quenching filler 8 I, while the other chamber contains theend portions 1| and 13 of the link, the heat softenable material 15, theopening means 11 and the inner end of contact terminal 6|.

Referring now to Fig. 4 of the drawings, I have there illustrated a fuselink 83 which is provided with a pair of fusing portions 85 near therespective ends thereof. One end is divided by a longitudinal slot intotwo end portions 81 and 89 corresponding to the respective end portions1| and 13 of fuse link 63 in Fig. 3.

Referring now to Figs. 5 and 6 of the drawings, I have there illustrateda protector of the plug fuse type |01 including a body |09 which may bemade of electric-insulating material, such as porcelain, and which has acentral contact terminal I|| and a screw shell contact terminal ||3thereon. A fuse link 5 which may be of any suitable kind has one endheld in electrical engagement with the central contact in any suitablemanner, as by ordinary solder ||1.

The other end of the fuse link ||5 is held 'in electrical engagementwith a relatively massive heat-conducting member 9 which, as shown, maybe vof substantially L-shape, by a small mass |2| of heat-softenablematerial, such as a low melting point solder. 'Ihe other end of member||9 is electrically connected to the screw shell terminal in anysuitable manner as by a mass |23 of solder which may have a relativelyhigh melting point as compared to 12|.

That end 'of link l I5 which is held in electrical contactI with memberH9 lhas secured thereto one end of a biasing or opening means |25 which,as shown in Figs. 5 and 6 of the drawings, is a helical spring, theother end of which is hooked arcanes around a metal bar |21 held by theupper end of the porcelain member |09.

Referring now to Fig. 7 of the drawings, I have there illustrated amodification of the device shown in Figs. 5 and 6, the principaldifference being that the central contact terminal |33 in the body |09may be made relatively heavier than the center contact shown in Fig. 5either by enlarging the outer dimensions thereof or by reducing the sizeof an opening |35 therein, this opening |35 being adapted to receive oneend of the link |31 and a small mass |39 of heat softenable material. Aspring |4| of the same general type as was hereinbefore described inconnection with the device shown in Fig. 5 of the drawings has one endoperatively connected to that end of the link which is in electricalengagement with Contact terminal 33, while the other end of the link |31is electrically connected to a screw shell contact I3 in any suitablemanner as by a mass |42 of solder which has a relatively higherm'eltingtemperature than that of the holding means |39.

Referring now to Fig. 8 of the drawings, I have there illustrated astill further modification embodying, in addition to the other elementsalready hereinbefore described as to body and terminals, a fuse link |43having one end thereof in electrical engagement with a center contactand being held therein by any suitable means as by solder |45 ofrelatively high melting point, while the other end thereof is held inelectrical engagement with a relatively heavy heat conducting memberI41, by a small mass of heat softenable material |53, such as lowmelting point solder. Instead of using a helical spring to break theelectrical contact between one end of the link |43 and the massive heatconducting member |41, I may use a leaf spring |49, one end of which maybe embedded in a small recess |5| in the body |09, while the movable endthereof interts with the other end of the link |43 so that whenpermitted to do so by softening of the small mass of heat-softenablematerial |53 normally holding the end of the fuse link in contact withmember |41, this electric conducting engagement may be broken.

The operation of the device shown in Fig. 1 is as follows: If a currentbe passed through the protector, heat will be generated in the fuse linkI and the other parts of the device l'traversed by the current but theother parts are so heavy and of such good conducting material that thefuse link is the main source of heat in theV protector. Moreover it isthe only element therein purposely designed to serve as a source ofheat. Accordingly whenever in the specification and claims the link isreferred to as being substantially the sole source of heat in theprotector, it is to be interpreted as having the above meaning. Part ofthis heat will cause a rise of temperature of the link and part will beconducted to the terminals, causing a rise in temperature of theterminals and intermediate parts including the heat softenable material.

When the protector is traversed by heavy overload currents some portionof the link may reacn fusing temperature and the link may blow in whichcase the protector acts as a fuse. This fusing portion may or may notdiffer in area of cross section or in material or in any other mannerfrom the remaining parts of the link; in those links where it does notdiffer the fusing portion will be substantially midway between the endsof the link. Opening of the circuit by the protector operating as a fusewill occur on short circuit and on all currents in excess of apredetermined value.

The heat softenable material which I use is one which loses its holdingpower at a tempera.- ture below the fusing temperature of the link andwhen the protector carries currents within a certain range below theabove mentioned value, suificient heat may be conducted to the heatsoftenable material to cause it to lose its holding power before anyportion of the link has reached fusing temperature. When this happens,the biasing or opening means becomes operative to open the circuit inthe protector by breaking the electrical connection normally maintainedby the heat softenable material by moving an end portion of the linklaterally, the protector therefor providing a thermally controlledmechanicallyoperable circuit interrupter which may open the circuitthrough the protector under certain operating conditions. Currents ofstill lower range of values will be carried by the protector withoutopening the circuit.

The heat softenable material is shown as being in good heat conductingrelation with both the link and one' contact terminal, so that it canreadily receive heat from the link and so that the length of timerequired for it to reach a temperature at which it loses its holdingpower may be increased by heat conducted from it to the terminal, theamount of heat conducted away from the heat softenable material beingincreased by the relatively heavy mass of material interposed betweenthe contact terminal.

It will thus be seen that the fuse link used in my device has a currentcarrying capacity greater than the current carrying capacity of theprotector as a whole and on very heavy overloads the device will openthe circuit almost instantaneously, while on lower overloads a longtime' lag is obtained, which time lag may be varied through aconsiderable range of magnitude by varying the heat conduction betweenthe heat softenable material and the contact terminal. In other wordsthe operation of the opening means is controlled by the holding meansand that of the holding means is controlled by the link, the control bythe link being modified by the amount of heat conduction provided forbetween the holding Imeans and one terminal.

The operation of the modifications shown in the other figures of thedrawings is the same as for the device of Fig. l although minorvariations are shown. In Fig. 3 of the drawings the heat absorbing massas a separate member between the heat softenable material and theterminal is omitted, the inwardly extending end of the terminal,lengthened if desired, serving as the equivaient thereof, and an endportion of the link is shown as bridging the circuit interrupter. Inthis modication the opening oi' the circuit interrupter does notinterrupt the total current through the protector but only that portionthereof flowing through the interrupter. After the interrupter has`operated the total current flows through the bridging portion of thelink which portion fuses almost instantaneously and .thus opens thecircuit through the interrupter. In order that this bridging portion ofthe link may operate in this manner, it is made of such cross sectionalarea that its`current carrying capacity will be small enough to causefusing thereof on J any current which will cause opening of the circuitinterrupter.

the heat softenable material and The obiect of this bridging member isto prevent destructive arcing at the interrupter contacts and to causethe final break to take place in an arc quenching filler, such as shownin Fig.

3, which may be desirable when the protectors are of relatively highrating.

It may be noted that the method of connecting the opening means is` suchthat it carries substantially no current and that the fusing portion ofthe link is substantially free from stress caused by the opening means.

While the drawings show preferred forms of protectors embodying myinvention, I do not desire to be limited to these particularcombinations or embodiments. For example, I have referred to and shownin the drawings, a small mass of heat softenable material normallyholding a portion of the fuse link in electric connection with oneterminal as a low melting point solder, but this may be any electricconducting or non-conducting material which is capable of holding thecooperating contact members of the circuit interrupter in electricalconnection at temperatures up to a certain value and which loses itsholding power when heated to, a temperature above said predeterminedvalue. For purposes of convenience this material is referred to in thespecification and the claims as a heat softenable materia Thisexpression is to be interpreted as covering any material capable ofmaintaining said electrical connection at all temperatures below apredetermined value and rendered incapable of maintaining suchelectrical connection when heated to a temperature above saidpredetermined value, irrespective of whether the loss of holding powerresults from softening or from any other physical change accompanying anincrease in its temperature.

I have shown the biasing or opening means as a helical spring in somefigures and as a leaf spring in another figure, but desire it to beunderstood that I may use any suitable means capable of beingoperatively combined with the other parts of the device and effective toopen the interrupter as described when the holding means 'has lost itsholding power.

While I have shown a heavy heat conducting member for conducting heatfrom the heat sof. tenable member, in Fig. 1 of the drawings, and haveshown the heat softenable material directly associated with a knifeblade terminal in Fig. 3 of the' drawings, I may omit the heavy memberfrom Fig. 1, or use its equivalent in Fig. 3 by making the inner portionof the contact terminal of Fig. 3 longer, the use or omission of thismember and its size, if used, being dependent on the time lag desired.

An arc quenching filler may be used or not, but where it is used theenclosure is dividedinto two chambers by a disc to keep the filler awayfrom the interrupter opening means.

' I do not desire to be limited to the forms of fuse links shown in thedrawings, but may use any form of fuse link and may make it .of anymaterial suited for the purpose. I may, if I nnd it desirable ornecessary to get the relatively long time lag desired, use fuse linksmade of metals having higher melting points than ordinarily Aused infuses. If such metals as copper, silver are not possible in a protectorembodying my d aisance invention, as the circuit will be opened by thecircuit interrupter, as hereinbefore described, before such unsafetemperatures can be reached.

The fusible member bridging the circuit interrupter in Fig. 3 may beused in the device shown in'Fig. l, or it may be omitted from thedevicev shown in Fig. 3. This member is shown in the drawings as anintegral part of the fuse link, but it would be within the spirit andscope of my invention to make it a separate member electricallyconnected to the link and bridging the circuit interrupter if I sodesire.

All of the devices illustrated and described in "the specificationembody the same inventive coneffective to move the portion of the linkto open circuit position when the holding means has been heated by thelink to a temperature at which it loses its holding power. Provision isalso made in all of these devices` to conduct heat away from the holdingmeans to thereby increase the time lag at overloads where the opening ofthe circuit is contingent on the opening of the circuit interrupter.

The fact that the fusing portion of the fuse link is substantially freefrom stress caused by the interrupter operating means, is an importantelement in my invention. It prevents injury and strain on the fusingportion and permits of obtaining closer and more uniform rating ofsimilar' fuses in mass production and the use of a weaker interrupteropening means. This use of a weaker `interrupter opening means precludesthe occurrence of fatigue in the holding means with consequent changesin the operating characteristics of the protector.

The fuses in my invention are designed for the protection of light andpower circuits and while there are some similarities between the fusesbuilt under my invention and some of the fuses called telegraph andtelephone fuses, there is an immense difference between them. Thetelegraph and telephone fuses are designed for small currents and are adistinct type of fuse wholly outside the eld of general industrial use.Most of them are so designed that if a fuse link heavy enough to carrycurrent values such as must be carried by fuses used in industrialservice were to.be used, the springs would have to be so heavy that itwould be impossible to enclose the protector element includingy such aspring in a casing of standard size for fuses of its rating. Most of thedevices of this general kind known to me and using a spring have thespring connected in series circuit with the link with'consequentpossibility of annealing the spring when subjected to heavy overloadsand thereby rendering the device inoperative unless a spring so large asto be prohibitive because of its size is used. A heavy spring, if used,would subject a part of the link and the heat softenable material tosuch stress as to render diilicult, or impossible, exact rating of theprotector and maintenance of initial rating during the life of thedevice. Again many suchvdevices known to me have electrical contactsdepending for their maintenance' on spring tension and not soldered orotherwise permanently connected and a construction of this kind makesfor uncertain operation at all times and more especially if the deviceremains in circuit for a relatively long time without opening and theabutting surfaces become more or less oxidized or corroded as is usuallythe case.

Bymy invention I am enabled to produce a commercially operativeprotective device of a size and external dimensions in conformity withpresent standard requirements forenclosed fuses and of such design andconstruction that it can be accurately rated and that it will maintainsuch rating throughout its entire time of being connected in an electriccircuit which it is to protect.

A protector embodying my invention will have much greater time lags onordinary overloads than fuses heretofore used, while at the same timeremaining capable of substantially instantaneously interrupting acircuit under short circuit conditions.

Although I have shown and described certain specific embodiments of myinvention, I am fully aware that other modifications thereof arepossible. My invention therefore is not to be restricted except insofaras is necessitated by the prior art and by the scope of the appendedclaims.

I claim as my invention: l

l. A protector for electric circuits comprising contact'terminals, afuse link electrically connected to the lterminals and adapted to fuseat a predetermined temperature and a thermallycontrolled mechanicallyoperable circuit interrupter, a portion of said fuse link constituting amovable contact member of said interrupter, a small mass of heatsoftenable material positioned relative to said portion of the link andthe cooperating terminal to normally hold them in electrical connectionwith each other to provide a path of low thermal reluctance for thetransfer of heat therebetween, said mass being adapted to lose itsholding power at a temperature below said predetermined temperature andmeans for opening the circuit interrupter when said mass of material haslost its holding power, the link being substantially the sole source ofheat in the protector, the link having a fusing portion substantiallyfree from stress caused by the interrupter operating means.

2. A protector for electric circuits comprising contact terminals, afuse link electrically connected to the terminals, a small mass of heatsoftenable material in contact with a portion only of said link and ingood heat conducting relation with one of said terminals to maintainsaid electrical connectionat all temperatures up to a predeterminedvalue, said mass being adapted to be heated by heat conducted to it fromthe link and to have the length of time required for it to be heated tosaid predetermined temperature to be increased by conduction of heatfrom it to said terminal and means for breaking said electricalconnection normally maintained by said heat softenable material when theheat softenable material has been heated to a predeterminedtemperature,'said connection breaking means being substantially freefrom current iiow therethrough, said fuse link being substantiallyA thesole source of heat in the protector, the link having a fusing portionsubstantially free from stress caused by the connection breaking means.3. A protector for electric circuits comprising contact terminals, afuse link electrically connected to the terminals, a small mass ofheatsoitenable material in contact with a portion only of said link andin good heat conducting relation with one of said terminals to maintainsaid electrical connection at all temperatures up to apredeterminedvalue, said mass being adapted to be heated by heat conducted to it fromthe link', and means to move said portion of the link to break saidelectrical connection normally maintained by said heat softenablematerial when it has been heated to said predetermined temperature, thelink being substantially the sole source of heat in the protector andhaving a fusing portion substantially free from stress caused by theconnection breakingfmeans.

A4. A protector for electric circuits comprising contact terminals, afuse link electrically connected to the terminals, a small mass ofheatsoitenable material normally maintaining the electrical connectionof the link to one terminal, said mass being in good heat conductingrelation with said one terminal, and means to cause substantiallylateral movement of a portion of the link to break said electricalconnection normally maintained by said heat-softenable material when thesame has been heated to a predetermined temperature, lsaid fuse linkbeing adapted to fuse at a predetermined current and constitutingsubstantially the sole means to heat said mass to said predeterminedtemperature when the link is traversed by currents of lower value thansaid predetermined value, the link having a fusing portion substantiallyfree from stress caused by the connection breaking means.

5. A unitary protector for electric circuits comprising a fuse link,electrically conducting means comprising a terminal contact face vand asupport for the link in permanently fixed low resistance thermalrelation, thermallyreleasable means adapted to hold a portion of tlielink in electrical connection with said support, a member having aterminal contact face, ilxed means for connecting another portion of thefuse link to said member, means adapted to move a portion oi the fuselink substantially transversely to open the circuit when the holdingmeans becomes releasable, said fuse link being substantially the solesource of heatfor the holding means.

6. A protector for electric circuits comprising a casing, contactterminala a fuse link electrically connected to the terminals, a mass ofheat softenable materialvv normally maintaining the electricalconnection of the link to one terminal Awhen the temperature of the heatsoftenable ma- Apredetermined temperature, the link being substantiallythe sole source of heat for the heatsoftenable material, the link havinga fusing por- -tion substantially free from stress caused by the biasingmeans.A

7. A protector for electric circuits comprising a casing, contactterminals, means substantially enclosing in the casing electricallyconnecting said terminals with each other including a fuse link, athermally-controlled-mechanically-operable circuit interrupter and arelatively heavy mass of good heat conducting material directly engagingone terminal, fthe circuit interrupter including a portion of said fuselink, said mass of good heat conducting material, a small mass of heatsoftenable material in contact with said portion of the link and withthe relatively heavy mass of good heat conducting material, and normallyholding the interrupter in' closed circuit the holding means becomes relposition and means for opening the circuit interrupter, said means beingsubstantially free from current ilow therethrough, said heat conducting.member remaining stationary during opening oi the interrupter, the fuselink being substantially the sole source of heat in the protector.

8. A unitary protector for electric circuits comprising a fuse link,means comprising a terminal contact face and a support for the linkpermanently ilxed in low electrical resistance relation, thermallyreleasable means adapted to hold a portion of the link in electricalconnection with said support, a member having a terminal contact face,xed means for connecting another portion of the fuse link to saidmember, means adapted to move a portion of the fuse link substantiallytransversely to open the circuit when able, said fuse link beingsubstantially the sol source of heat for the holding means.

9. A protector for electric circuits comprising contact terminals, afuse link electrically connected to the terminals, said link beingeffective to open a circuit therethrough by fusing on some portionthereof when carrying a current in excess of a predetermined value, asmall mass of heat softenable material in engagement with both said linkand one of said terminals for normally maintaining the electricalconnection of the link and said one terminal, said link beingsubstantially the sole source of heat in the protector and causingheating of the mass of heatsoftenable material and a reduction oi' itsholding power on the passage through the link for a relatively longperiod of time of a current too small to fuse the link and means to movea portion of the link to break said electrical connection normallymaintained by said heat-soltenable material when the holding power ofthe mass of heat softenable material has been reduced below' apredetermined value.

10. A protector i'or electric circuits comprising contact terminals, arelatively heavy good electric and heat-conducting member engaging oneterminal, a fuse link electrically connected to said goodheat-conducting member and eilective to open a circuit therethrough byfusing in some portion thereof when carrying a current in excess oi apredetermined value, a small mass of heat softenable material engagingboth the heavy heat conducting member and the fuse link to normallymaintain the electrical connection therebetween, the link beingsubstantially'the sole source oi' heat in the protector and causingheating of the mass of heat softenable material and a reduction of itsholding power on the passage through the link for a relatively longperiod of time of a current too small to fuse the link, and means tobreak said electrical connection between said link and said relativelyheavy heat conducting member when the holding power of the mass ofheatsoftenable material has been reduced below a predetermined value,the link having a fusing portion substantially free from stress causedby the connection breaking means.

1l. A protector for electric circuits comprising a casing, contactterminals and means substantially enclosed in the casing electricallyconnecting said terminals with each other, said means including a fuselink constituting substantially theV sole source of heat in theprotector and a thermally-controlled-mechanically-operable circuitinterrupter, a portion of said fuse link constituting a movable contactmember of said interrupter, a small mass of heat softenable materialholding said link in closed circuit position and being in good heatconducting relation with one of said terminals, said mass being adaptedto be heated by the link and to lose the holding power when heated to apredetermined degree and means substantially free from current flowtherethrough, effective to move said portion of the link to open circuitposition when the heat softenable material has lost its holding power.

12. A protector for electric circuits comprising a casing, contactterminals and means substantially enclosed in the casing electricallyconnecting said terminals with each other, said means including athermally-controlled-mechanicallyoperable circuit interrupter adapted tooperate at current values within a predetermined range oi magnitude, anda fuse link adapted to fuse in some portion thereof at currents inexcess of said predetermined range of magnitude, said interrupterincluding a portion of said fuse link, a small mass'of heat softenablematerial in contact with a portion only of said link and in good heatconducting relation with one of said terminals normally holding theinterrupter in closed circuit position and means to move said portion ofthe link to open the circuit interrupter on softening of the heatsoftenable material to a certain degree, said link being substantiallythe sole source of heat for the heat softenable material, the linkhaving a fusing portion substantially free from stress caused by thecircuit interrupter opening means.

13. A protector for electric circuits comprising Contact terminals, afuse link electrically connected to the terminals, and athermally-controlled-mechanically-operable circuit interrupter includinga portion of said fuse link and means normally holding the interrupterin closed circuit position, said holding means being in good heatconducting relation with one of said terminals, means for opening thecircuit interrupter, the holding means being controlled by the fuse linkand the action of the opening means being controlled by the holdingmeans and a relatively heavy mass of heat absorbing material in contactwith the holding means to modify the control of the holding means bysaid fuse link, the fuse link being substantially the sole source ofheat on the protector, and having a fusing portion substantially freefrom stress caused by the opening I means, said mass of heat absorbingmaterial remaining stationary during opening of the circuit interrupter.

14. A protector for electric circuits comprising contact terminals,arelatively heavy good Aelectric and heat conducting member engaging oneterminal, a, fuse link adapted to fuse at a predetermined temperature,and having a portion engaging said relatively heavy good heat conductingmember, a small mass of heat softenable material in intimate contactwith said relatively'heavy heat vconducting member and the link normallyholding said parts in electrical engagement with each other and adaptedto be heated and to lose its holding power at a temperature ,below thatat which fusion of the link occurs, the link being substantially thesole source of heat for the heat softenable material, the length of timerequired for the heat-softenable material to reach a given temperaturebeing increased by the conduction of heat therefrom by the relativelyheavy member, means effective to move said portion of the link to opencircuit position on softening of the heat softenable material to acertain degree, the link having a fusing portion substantially freeamarres from stress caused by the link-moving means.

15. A device as set forth in claim 4 and including a cartridge casinghaving a disc therein dividing the interior thereof into two parts, onepart containing an arc quenching ller and the major portion of the fuselink including the fusing portion thereof and the other part containingan end portion of the link and the circuit interrupter, including thesmall mass of heat softenable material and the connection-breakingmeans.

16. A device as set forth in claim 4 and including a cartridge casinghaving a disc therein dividing the interior thereof into two parts, onepart containing an arc quenching filler and the major portion of thefuse link including the fusing portion thereof, the other partcontaining an end portion of the link and the circuit interrupter,

the circuit interrupter including said end portion of the link, theinterrupter operating means being a relatively light spring having oneend engaging said end portion of the link and its other end connected toa part of the protector structure.

17. A device as set forth in claim 10 and including a cartridge casinghaving a disc therein dividing the interior thereof into twov parts, onepart containing an arc quenching filler and the major portion of thefuse link including the fusing portion thereof, the other partcontaining the heat conducting member, an end portion of the link, thesmall mass of heat softenable material and the connection breakingmeans.

18. A device as set forth in claim 1 and including a cartridge casinghaving a disc of electric insulating material therein dividing theinterior thereof into two parts, one part containing the fusing portionof the link and an arc quenching filler, the other part containing thecircuit interrupter.

19. A protector for electric circuits comprising contact terminals, afuse link having a portion adapted to fuse at a predeterminedtemperature and in direct contact with one of said terminals, a smallmass of heat softenable material in intimate heat transferring relationwith said link and its contacting terminal to normally hold said link inelectrical engagement with said terminal and adapted to be heated and tolose its holding power at a temperature below that at which fusion ofthe link occursy-the link being substantially the sole source of heatfor the heat softenable material, the length of time required to'raisethe temperature of the heat softenable material being increased by theconduction of heat therefrom by the cooperating terminal, andmeanseffective to move said link to interrupt the circuit in the protector onsoftening of the heat softenable material to a certain degree.

20. A protector for electric circuits comprising a fuse link and amechanically operable circuit interrupter, a portion of said linkconstituting a contact member of the interrupter, said inter- 'rupterincluding also means in contact with said normally holding an endportion of said link in electrical contact with said terminal, a heatconducting path of low resistance between the heat softenable materialand the terminal remaining in fixed position during operation of theprotector, and means engaging said end portion of the link to causesubstantially transverse movement thereof to open the circuit in theprotector when the holding means has lost its holding power.

22. A protector for electric circuits comprising a fuse link, athermally controlled mechanically operable circuit interrupter adaptedto open when heated above a predetermined temperature and a memberbridging the circuit interrupter and adapted to open the circuit in theprotector by fusing after the interrupter has opened, said member beingadapted to fuse at any current which will open said interrupter.

23. A protector for electric circuits comprising a fuse link, athermally-controlled-mechanicallyoperable circuit interrupter includinga small mass of heat fsoftenable material normally holding theinterrupter in closed position and adapted to lose its holding powerwhen heated to a predetermined temperature, said interrupter beingadapted to open when said mass has been heated to said predeterminedtemperature and a member bridging the circuit interrupter and adapted toopen the circuit in the protector by fusing after the interrupter hasopened.

24. A protector for electric circuits comprising a fuse link, athermally controlled mechanically operable circuit interrupter adaptedto open when heated above a predetermined temperature and meansincluding a portion of the fuse link bridging the circuit interrupterand adapted to open the circuit in the protector by fusing after theinterrupter has opened, said portion of the link being adapted to fuseat any current value at which the interrupter will open.

25. A protector for electric circuits comprising a fuse link adapted tofuse when traversed by currents in excess of a predetermined value andhaving a portion adapted to fuse when traversed by currents below saidpredetermined value and means including a thermally controlledmechanically operable circuit interrupter to cause a predetermined timedelay in the fusing of said portion of the link, said portion of thelink fusing only after the interrupter has opened and being adapted tofuse at any current value at which the interrupter will open.

26. A protector for electric circuits comprising a fuse link adapted toopen the circuitby fusing in relatively short times when the protector'is traversed by currents in excess of a predetermined value, athermally-controlled-mechanically-operable circuit interrupter adaptedto open in longer times when the protector is traversed by currents ofless than said predetermined value but greater than a second lowerpredetermined value and means including a portion of said fuse linkadapted to open the circuit by fusing after opening of the interrupter,at any current through the protector which will open said interrupter.

27. A protector for electric circuits comprising a casing, contactterminals and means electrically connecting said terminals in thecasing, said means including a fuse link and athermally-controlledemechanically-operable circuit interrupter, saidinterrupter comprising an end portion of the link constituting a'movablecontact member thereof, a small mass of heat softenable material in goodheat conducting relation with both said end portion of the link and oneof said terminals, holding said end portion of the link in closedcircuit position and adapted to lose its holding power when heated to apredetermined temperature and operating means acting on said end portionof the link and adapted to move it to open circuit position when theholding means has lost its holding power and a second end portion of thelink normally bridging the interrupter and adapted to open the circuitin the protector after the opening of the interrupter.

28. A protector forelectric circuits comprising a casing, contactterminals and means electrically connecting said terminals in thecasing, said means including a fuse link and athermally-controlled-mechanically-operable circuit interrupter, saidinterrupter comprising an end portion of the link constituting a movablecontact member thereof, a small mass of heat softenable material in goodheat conducting relation with both said end portion of the link and oneof said terminals, holding said end portion of the link in closedcircuit position and adapted to lose its holding power when heated to apredetermined temperature and operating means engaging said end portionof the link and adapted to move it in a direction substantiallylaterally of the link to open circuit position whenv the holding meanshas lost its holding power and a second end portion of the link normallybridging the interrupter and adapted to open the circuit in theprotector after the opening of the interrupter.

29. A protector for electric circuits comprising a casing, contactterminals, means substantially enclosed in the casing electricallyconnecting said terminals with each other, said means including a fuselink, a thermally-controlled-mechanically-operable circuit interrupterand a member bridging the circuit interrupter and adapted to open thecircuit in the protector by fusing after the interrupter has opened andan arc-quenching ller in the casing surrounding the fusing portions ofsaid fuse link and bridging member.

30. A protector for electric circuits comprising a casing, contactterminals, means substantially enclosed in the casing electricallyconnecting said terminals with each other including a fuse link, athermally-controlled-mechanically-operable circuit interrupter and arelatively heavy mass of good heat conducting material comprising aninwardly extending portion of one of said terminals, the circuitinterrupter including a portion of said fuse link, said mass of goodheat conducting material, a small mass of heat softenable material incontact with said portion of the link and with the relatively heavyterminal mass of good heat conducting material, and normally holding theinterrupter in closed circuit position and means for opening the circuitinterrupter, said means being substantially free from current flowtherethrough, said heat conducting member remaining stationary duringopening of the interrupter. the fuse link being substantially the f solesource of heat in the protector.

31. A protector for electric circuits comprising a fuse link adapted tofuse and open the circuit on currents in excess of a. predeterminedvalue, a thermally. controlled mechanically operable circuit interrupteradapted to open on currents of lower value and a member bridging thecircuit interrupter adapted to remain unfused on currents in excess ofsaid predetermined value and to open the circuit by fusing on currentsbelow u aimeras said predetermined value after the interrupter hasopened, said member being adapted to fuse on any currentl which willopen the interrupter. 32. A protector for electric circuits comprising ia fuse link adapted to fuse on currents above a predetermined value annihaving a portion adapted to remain unfused on said currents

